Black Spots on Angraecum - Please Help!

[HiOrcDen]

I have a very large Angraecum which started developing very small black spots, surrounded in yellow, soon after I purchased it. I thought this was a sign of sunburn. Though my lower light requirement plants were doing fine in the same level of shade, I thought these spots may have come from a small gap by the shade cloth, or perhaps this plant being too close to a wall.

My Orchids are temporarily inside, with full spectrum lights, near an open north-facing window, for fresh air. The weather is moderate. The spots had stopped accumulating, for a good while, but now the Angraecum has developed a few more. They are all on leaves halfway down or lower. I have researched on the web, and if not sunburn, I understand it might be a fungus or a bacteria. I have taken measures to make sure there is good air circulation and drainage.

How will I know if things are too far gone to the point of needing to check for and clip rotted roots, or cut out spots?

I have something called Bio Advanced 3 in 1, in a spray bottle. Is this okay for an orchid, and could it help? I've also read that hydrogen peroxide may help. Should I apply either or both of these? Is there another product specifically for orchids which will work well? And if I buy it, again, should I use the hydrogen peroxide (in which case at what concentration) or Bio Advanced 3 in 1 in the meantime?

[Roberta]

Bio Advanced is the new formulation that used to be Bayer's 3-in-1 ... It has an insecticide, a miticide, and fungicide so covers a lot of territory. Spray bottle is fine for small collection... I'd get the concentrate, a much better deal. Don't rush to cut anything.

[estación seca]

Angraecums and relatives moved from high humidity to low humidity frequently get black spots.

[HiOrcDen]

Originally Posted by Roberta

Bio Advanced is the new formulation that used to be Bayer's 3-in-1 ... It has an insecticide, a miticide, and fungicide so covers a lot of territory. Spray bottle is fine for small collection... I'd get the concentrate, a much better deal. Don't rush to cut anything.

So I used this formula (and I had the concentrate ) I'm afraid I may have used it too often. Well I'm not sure... either overuse of the spray, or a little stubbornness of the spots, which had not spread to upper leaves, but I caught one higher up today. I had a Japanese Red Maple that I think I killed by using too much of the stuff.

Originally Posted by estación seca

Angraecums and relatives moved from high humidity to low humidity frequently get black spots.

Okay that is good to know. So if it is what you describe, I hope it's not as harmful as a rot? How would I treat this?

Also may I ask you both, since I'm not supposed to use the Bayer more than once every week or two, could I use a hydrogen peroxide solution? If so, what concentration and frequency is safe? (and should I be concerned if it's the low humidity issue, and not rot from excess moisture, and how would I treat?)

[Roberta]

You need to know what you are treating before applying treatment. Peroxide is not likely to be useful. Myself, I don't worry about dings on leaves. If you have a specific pest (like scale) and need to use a pesticide, you'd want to treat about once a week for 3-4 weeks with a pesticide. Best to have more than one to rotate, to not create resistance. Fungal problems need a fungicide. Mites need a miticide. You don't take antiobiotics for a cold...

Overall, concentrate on your cultural conditions.

[estación seca]

Agree. 2 important points:

• Don't treat with chemicals unless you know exactly what the disease or pest is and know the chemical treats that problem;
• Unless relative humidity is very high and/or temperatures are far from correct disease is unlikely.

Most leaf spotting and browning are from incorrect growing conditions, not diseases.

[HiOrcDen]

Originally Posted by Roberta

You need to know what you are treating before applying treatment. Peroxide is not likely to be useful. Myself, I don't worry about dings on leaves. If you have a specific pest (like scale) and need to use a pesticide, you'd want to treat about once a week for 3-4 weeks with a pesticide. Best to have more than one to rotate, to not create resistance. Fungal problems need a fungicide. Mites need a miticide. You don't take antiobiotics for a cold...

Overall, concentrate on your cultural conditions.

Originally Posted by estación seca

Agree. 2 important points:

• Don't treat with chemicals unless you know exactly what the disease or pest is and know the chemical treats that problem;
• Unless relative humidity is very high and/or temperatures are far from correct disease is unlikely.

Most leaf spotting and browning are from incorrect growing conditions, not diseases.

Okay, so as far as conditions, I may be erring one way, or the opposite way. Since the plants are temporarily inside, then is it possible the problem relates to not enough temperature differential between day and nigh? On the other hand, is it possible a cold draft from a nearby open window has had the opposite negative affect?

So now I'm thinking I should keep that window open, and not too wide, to simplify matters

[Roberta]

Day-night temperature differential pretty much applies to blooming... not enough and it doesn't. (and different for different orchids, tropical ones don't need much and more temperate zone ones need more) Air movement is important - reduces chance of various pathogens getting a foothold. I would not worry about cold particularly where you (we) live. Nights are not particularly cold this time of year. Maybe you're seeing the results of cold from some time ago? Or maybe you have nothing to worry about at all. (Most of my orchids have ugly leaves but they grow and bloom well)

[estación seca]

The few Angraecums I've grown got spots from underwatering, low humidity, sunburn or low temperatures. But low is relative, because different species have very different temperature / light / humidity in habitat.